Method for obtaining high-tenacity aramid yarn

ABSTRACT

The invention relates to a method for obtaining high-tenacity aramid yarn, wherein the yarn is made of a copolymer obtained from a mixture of monomers comprising DAPBI, an aromatic para-diamine, and an aromatic para-diacid, wherein the yarn is heated in at least two process steps, characterized in that in a first step the yarn is heated at a temperature of 200 to 360° C. at a tension of at least 0.2 cN/dtex, followed by a second step wherein the yarn is heated at a temperature of 370 to 500° C. at a tension of less than 1 cN/dtex. The invention further pertains to a multifilament aramid yarn spun from a sulfuric acid spin dope and having a tenacity of at least 2500 mN/tex.

This is a Divisional Application of application Ser. No. 12/311,654filed Apr. 8, 2009, now issued as U.S. Pat. No. 8,501,071, which is aNational Phase of PCT/EP2007/009901 filed Nov. 19, 2007, and whichclaims priority to European Application No. 060241049, filed Nov. 21,2006. The disclosures of the prior applications are hereby incorporatedby reference herein in their entireties.

The invention relates to a method for obtaining high-tenacity aramidyarn, wherein the yarn is a copolymer obtained from a mixture ofmonomers comprising DAPBI, an aromatic para-diamine, and an aromaticpara-diacid, and wherein the yarn is heated in at least two processsteps.

Methods of heat treating yarn of spun copolymer obtained from a mixtureof monomers comprising DAPBI(5-(6)-amino-2-(p-aminophenyl)benzimidazole) and PPD (para-phenylenediamine) in a heating oven are known in the art. Typically, as-spunyarns are led through an oven at a temperature of about 450° C. Theresidence time of the yarn in the oven is controlled by the yarn speedand is usually set between 20 seconds and 5 minutes at controlledtensions between 0.2 and 1 cN/tex. Such method using a single heatingstep is for example known from CN 1473969. Methods of heat treating spunDAPBI-PPD copolymer yarn in two separate process steps are also known inthe art. In the Russian patent RU 2017866 a two step heat treatment isdisclosed. These polymers are subjected to a draw-out step up to 120 wt%, followed by wash and drying steps, followed by a heat treatment at320 to 350° C., and a further drawing at 360 to 420° C. to 1-3 wt %. Thefirst heat treatment step is carried out with the yarn on the bobbin byplacing the bobbin in an oven for 30 minutes. In this method the yarntension cannot be controlled and heat treatment times of the differentlayers of yarn on the bobbin will differ due to heat transport timethrough layers of yarn.

Thermal drawing was disclosed in Sugak et al., Fibre Chemistry, Vol. 31,No. 1, 1999. Heating was performed in a heating zone, and in additionthe fibers were heated (at undisclosed temperature) when the sampleswere wound on spools. However, heating the yarns during the process ofreeling-up will lead to an uncontrolled process which unfavorablycontributes to the properties of the yarn. In RU 2045586 a similarprocess was disclosed wherein the filaments were reeled up, washed anddried, and as such heated at 350-370° C., and thereafter hot-drawn at390-400° C. Yarns with high tenacity could be prepared, however, onlywith optimum amounts of DAPBI and Cl-PPD (2-chloro-p-phenylenediamine).Thus example 20 provides high tenacity yarn using 7.5 mole % DAPBI and25 mole % Cl-PPD. RU 2045586 further teaches that any increase of DABPIcontent and/or any decrease of Cl-PPD content leads to decrease oftenacity. It was further found that tenacities of at least 2500 mN/texcould only be obtained in the presence of Cl-PPD (at least 20 mole %).It is stressed that using Cl-PPD and certainly higher amounts thereof,is less preferred because of the presence of chlorine since it mayunfavorably affect the properties of the yarn when heat is used.

Again, the uncontrolled first heat treatment on the bobbin willunfavorably contribute to the final properties of yarn having highamounts of DABPI or low amounts of Cl-PPD.

It is therefore an objective of the present invention to provide amethod that does not have the disadvantages of the known two-stepheating processes, whereas the properties of the yarn having relativelyhigher amounts of DABPI and/or lower amounts of Cl-PPD are much betterthan as obtained by the conventional one-step method.

To this end the invention pertains to a method for obtaininghigh-tenacity aramid yarn, wherein the yarn is a copolymer obtained froma mixture of monomers comprising DAPBI, an aromatic para-diamine, and anaromatic para-diacid, wherein the running yarn is heated in at least twoprocess steps, characterized in that in a first step the yarn is heatedat a temperature of 200 to 360° C. at a tension of at least 0.2 cN/dtex,followed by a second step wherein the yarn is heated at a temperature of370 to 500° C. at a tension of less than 1 cN/dtex.

The new method consists of two different heating steps in two heatingzones, such as two sets of heating devices, such as ovens, or in oneoven having a temperature gradient.

In the first step the yarn is pre-drawn to a tension that is as high aspossible without disturbing the process. The temperature in this step ispreferably kept at 240° C. to 330° C. The first step is preferablydirectly followed by a second drawing step at preferably 400° C. to 470°C. under low tension. Between the two steps there is preferably nowinding and unwinding of the yarns. Preferably in both steps oxygenlevels are kept below 0.5 wt %, preferably at about 0.25 wt %.

For optimum yarn properties it is important that no further processsteps are performed between the two process steps. Thus for optimumresults it is important that no winding and unwinding of the yarn occursbetween the two process steps.

The yarn is led through the heating zones usually at a rate leading to aheat residence time of at least 5 seconds, preferably at least 10seconds, most preferably at least 20 seconds in both heating zones.

The yarn tension in the heating devices (such as ovens) is controlled bythe draw ratio in the ovens. In the second step the tension is kept aslow as possible without disturbing the transport of the yarn. Inpractice this is usually about 15 cN for a bundle of approximately 130dtex.

For obtaining the best results, i.e. the highest tenacities, the processsteps are performed under conditions wherein the tension is kept asconstant as possible. This can, for instance, be obtained by keeping theyarn speed fluctuations as small as possible.

It is further advantageous to use copolymers having a η_(rel) (relativeviscosity) of at least 3.5. The relative viscosity can be measured byknown methods, for instance as disclosed in EP1689805.

The monomers used for making the yarn of the invention comprise DAPBI,which stands for 5-(6)-amino-2-(p-aminophenyl)benzimidazole. The term“aromatic para-diacid” as used throughout this invention has the meaningaromatic para-diacid or derivative thereof. Usually the acid as such isnot used as monomer for the polymerization reaction but an ester orhalide thereof, more particularly the acid chloride is used.

The term “aromatic para-diamine” as used throughout this invention hasthe meaning aromatic para-diamine or derivative thereof. Examples arePPD, Cl-PPD, Me-PPD, MeO-PPD, and the like. Most preferably PPD and/orCl-PPD are used. Although DAPBI is also an aromatic diamine, thiscompound is not included in the definition of “aromatic para-diamine”.

The DAPBI-PPD copolymer is obtained by co-polymerizing the aromaticdiamine monomer 5-(6)-amino-2-(p-aminophenyl)benzimidazole and thearomatic para-diamine monomer p-phenylene diamine (PPD), and thearomatic para-diacid derivative terephthaloyl dichloride (TDC). Althoughnot required, part or all of the above para-aromatic monomers can bereplaced by other para-aromatic monomers, for instance part or all ofPPD can be replaced by PPD analogues, such as2-chloro-p-phenylenediamine (Cl-PPD), and TDC can be partly or fullyreplaced by Cl-TDC (2-chloroterephthaloyl dichloride).

Particularly useful yarns for use in this method are as-spun yarns.As-spun yarns are yarns that are spun but did not undergo a heatingtreatment at 200° C. or more. Particularly good results are alsoobtained for yarn (or as-spun yarn) obtained from a sulfuric acid spindope. Yarns obtained from a sulfuric acid spin dope have a sulfurcontent of at least 0.1 wt %. It is advantageous to use sulfuric acidspin dopes, since by using such spin dopes much higher spinning speedscan be obtained than when NMP- or DMAc-containing spin dopes are used.It is further preferred to have as low as possible hydrogen chloridecontents in the yarn to prevent release of hydrogen chloride from theyarn. Hydrogen chloride contents lower than 0.5 wt % are preferred. Mostpreferred are yarns that are totally or virtually free from hydrogenchloride.

According to a preferred embodiment of the method the first process stepis performed at 240 to 330° C. at a tension of at least 1 cN/dtex,preferably at least 3 cN/dtex. In principle, for obtaining the bestresults the tension is kept high during the first heat treatment. Thehighest possible tension is about 95 wt % of the breaking tension at thetemperature applied. At higher tensions the yarn will break. To preventany breakage it is preferred not to use tensions far above 90 wt % ofthe breaking tension at the temperature applied. Preferably theresidence time used is mostly at least 20 seconds.

According to a preferred embodiment of the method the second processstep is performed at 400 to 470° C. at a tension less than 0.2 cN/dtex.This tension is usually kept as low as possible. By using specialequipment, such as a conveyor belt, tensions of as low as 0 cN/tex (i.e.no tension at all) can be achieved. The residence time is mostpreferably at least 20 seconds.

The highest increase of the tenacity in comparison with the conventionalone-step method is obtained when the copolymer is made from a mixture ofmonomers wherein at least 12.5 mole %, preferably at least 17 mole % ofthe monomers is DAPBI. The copolymers can be prepared according to knownmethods, such as disclosed in U.S. Pat. No. 4,018,735 or WO 2005/054337.

The method according to this invention leads to aramid yarns havingfurther improved tenacity. It was found that this method can lead toyarns having tenacity of approximately 200 mN/tex higher thanconventionally produced yarns. It is therefore also an objective of theinvention to provide a multifilament aramid yarn having a tenacity of atleast 2500 mN/tex wherein the yarn is a copolymer obtained from amixture of monomers comprising DAPBI, an aromatic para-diamine, and anaromatic para-diacid wherein at least 12.5 mole % of the monomers isDAPBI, less than 20 mole % is Cl-PPD, and wherein the yarn has a sulfurcontent of at least 0.1 wt %. Preferably the mixture comprises monomerswherein at least 17 mole % of the monomers is DAPBI. Such high-tenacitymultifilament yarns spun from a sulfuric acid spin dope are not yetknown. In another preferred embodiment the mixture only contains PPD asthe aromatic para-diamine.

In an alternative embodiment according to the invention themultifilament aramid yarn has a tenacity of at least 2500 mN/tex whereinthe yarn is made of a copolymer obtained from a mixture of monomerscomprising DAPBI, an aromatic para-diacid, and an aromatic para-diaminewhich is exclusively PPD, wherein at least 12.5 mole % of the monomersis DAPBI, and wherein the yarn has a sulfur content of at least 0.1 wt%.

Preferably such multifilament aramid yarn has a tenacity of at least2750, more preferably 2850 mN/tex. The multifilament yarn has at least 2filaments. Most preferred multifilament yarns have at least 25filaments. Monofilament yarns have been previously disclosed in U.S.Pat. No. 4,018,735 having tenacity 30 gpd (about 2650 mN/tex) for 10mole % DAPBI (example 14) and 30.5 gpd (about 2690 mN/tex) for 25 mole %DAPBI (example 7). It should however, be born in mind that the tenacityin U.S. Pat. No. 4,018,735 was measured on the filaments, not on theyarn. These values therefore cannot directly be compared with thepresently claimed values. According to the standard textbook KevlarAramid Fiber, by H. H. Yang ((John Wiley & Sons, 1993, pages 34-35) thetenacity of yarn is usually 80-85 wt % of the tenacity of a singlefilament. This factor should be kept in mind when comparing yarnproperties with filament properties. Thus the filament values of U.S.Pat. No. 4,018,735 are in terms of the presently claimed yarn tenacitiesat the most about 2250 and 2290 mN/tex, respectively.

The invention is further illustrated by the following non-limitativeexamples.

General

The tenacity was measured according to the method described in ASTM D885

The Na, S, Cl and Ca contents are determined by XRF as follows.

Sample Pretreatment

The sample was ground to a fine powder in a Herzog HMS 100 grinding millwith a tungsten carbide grinding vessel. The aramid powder was pressedto a 20 mm diameter tablet by a Fontijne TP 400 plate press at 175 kNpressure for 2 minutes.

XRF Measurement

This measurement was performed with a PW2400 Philips X-ray fluorescencespectrometer and aluminum sample holders for 20 mm tablets

The following instrumental settings were applied:

X-ray tube: Chromium anode

Detector: Flow Counter for Ca, Cl, Na, S.

Filter: None.

Collimator mask: 16 mm

Medium: Vacuum

The instrumental settings were as follows:

back- PHD- 2θ ground colli- setting angle offset T_(p) T_(b) mator UL/LLLine kV mA (°) (°) (s) (s) Crystal μm wt % Ca-Kα 60 50 113.200 +/−2.0050 10 LiF200 150 80/20 Cl-Kα 60 50  92.810 +/−2.00 50 10 Ge 111 55070/30 Na-Kα 50 60  28.180 +/−2.00 50 10 PX1 700 80/20 P-Kα 60 50 140.994+/−1.60 50 10 Ge 111 550 80/20 S-Kα 60 50 110.680 +/−2.00 50 10 Ge 111550 80/20

The principle of quantification is based on a linear relationship ofNa-, S-, Cl-, and Ca—Kα-fluorescence intensities with knownconcentrations to give a calibration line, which line is used todetermine unknown concentrations.

EXAMPLE 1 Comparative: One-Step Process

A polymer obtained from a mixture of 25 mole % PPD and 25 mole % DABPI(and 50 mole % TDC) having η_(rel) 6.0 was dissolved in 99.8 wt %sulfuric acid, as described in WO 2006/045517. Zone temperatures in thetwin screw extruder were between 90 and 75° C. The polymer concentrationin the solution was 20 wt %, and the solution was spun through 50spinning holes of 75 micron. The spinneret assembly was kept at 125° C.The flow was drawn in an airgap and coagulated in water of 2° C. Afterwashing 0.5 wt % NaOH in water was used as neutralizing fluid, and in asecond washing step the neutralizing fluid was washed off. The yarn wasdried at 160° C. and reeled up at 147 m/min to obtain as-spun yarns.

This yarn has a linear density of 148 dtex, a tenacity of 1305 mN/texand a modulus of 65 GPa.

This yarn was submitted to drawing in an oven at temperatures rangingfrom 400 to 475° C. under nitrogen. The residence time in the oven was28 seconds in all cases. During this drawing various tensions wereapplied; ranging from 0.17 cN/dtex to 2.53 cN/dtex, as a result ofdrawing ratios between 1.01 and 1.03. The properties and the essentialmachine settings are given in Table 1.

TABLE 1 Tension in T Linear Elongation oven oven density Tenacity atbreak Modulus Toughness cN/dtex ° C. dtex mN/tex wt % Gpa J/g Untreatedyarn 148 1305 4.2   65 31 0.17 400 130 2065 2.80 122 31 1.40 400 1301959 2.43 131 25 2.83 400 127 1759 2.07 135 20 0.19 425 130 2338 3.09123 37 1.27 425 129 2108 2.56 131 28 2.53 425 128 1664 1.95 135 17 0.21450 132 2468 3.16 124 40 1.16 450 131 2212 2.61 134 30 2.38 450 130 16871.93 136 17 0.27 475 131 2438 3.10 126 39 1.20 475 131 2030 2.44 131 262.26 475 129 1472 1.68 135 13 The highest tenacity is achieved at 450°C. using the lowest tension applied.

EXAMPLE 2

As-spun yarns were prepared as described in Example 1. The yarn wassubmitted to a two-step heat treatment procedure in which the first stepwas carried out at lower temperatures (300 to 360° C.) than the secondstep (450° C.), and lower than in Example 1, and wherein the tensionapplied on the yarns were higher in the first step than in the secondstep. Between the two steps the yarns were not reeled up, buttransported by a godet that functions as a tension/speed control. Yarntensions in the second step were between 0.25 and 0.29 cN/dtex.Residence time in both heating zones was 28 seconds.

The yarn properties and essential machine settings are given in Table 2.

TABLE 2 Tension Tension Linear Elongation oven 1 oven 2 oven 1 oven 2density Tenacity at Break Modulus Toughness cN/dtex cN/dtex (° C.) (°C.) dtex [mN/tex] [wt %] [GPa] [J/g] as-spun yarn 153 1356 4.3  68 330.33 0.27 300 450 131 2603 3.3 124 43 1.63 0.26 300 450 131 2698 3.3 12744 3.68 0.28 300 450 130 2770 3.3 129 46 0.24 0.29 330 450 130 2652 3.3125 45 1.52 0.26 330 450 131 2698 3.3 128 45 3.40 0.25 330 450 131 26633.2 128 44 0.22 0.25 360 450 132 2601 3.4 122 45 1.44 0.26 360 450 1322696 3.4 125 46 3.15 0.25 360 450 133 2656 3.3 126 44

EXAMPLE 3

As-spun yarns were prepared as described in Example 1. The temperatureof the spinneret assembly was 91° C., the neutralization fluid had aNaOH concentration of 0.8 wt % and the winding speed was 140 m/min. Theas spun yarn had a linear density of 147 dtex, a tenacity of 1451mN/tex, a modulus of 62 GPa and a toughness of 35 J/g. The yarn wassubmitted to a two-step heat treatment procedure in which the first stepwas carried out at lower temperatures (260 to 300° C.) than the secondstep (450° C.). The temperature of the first step was also lower thanthe temperature of the first step in Example 2. The tensions applied onthe yarns were higher in the first step than in the second step. Betweenthe two steps the yarns were not reeled up, but transported by a godetthat functions as a tension/speed control. Yarn tensions in the secondstep were 0.1 cN/dtex. Residence time in both heating zones was 28seconds.

The yarn properties and essential machine settings are given in Table 3.

TABLE 3 Tension Tension Linear Elongation oven 1 oven 2 oven 1 oven 2density Tenacity at Break Modulus Toughness cN/dtex cN/dtex (° C.) (°C.) dtex [mN/tex] [wt %] [GPa] [J/g] 0.52 0.1 260 450 134 2730 3.67114.8 50.0 1.93 0.1 135 2720 3.64 116.6 49.8 4.22 0.1 132 2790 3.62118   50.5 0.46 0.1 280 450 133 2640 3.59 114.3 47.7 1.83 0.1 134 27103.58 117.4 49   4.03 0.1 134 2740 3.61 118.5 49.6 0.36 0.1 300 450 1362660 3.61 116.5 48.6 1.79 0.1 136 2600 3.6  113.8 48   3.99 0.1 137 27803.63 118.4 50.3

EXAMPLE 4

As-spun yarns were prepared according to Example 3, but the residencetime in both heating zones was increased to 56 seconds.

The yarn properties and the most essential machine settings are given inTable 4.

TABLE 4 Tension Tension Linear Elongation oven 1 oven 1 oven 1 oven 2Density Tenacity at Break Modulus Toughness cN/dtex cN/dtex (° C.) (°C.) dtex [mN/tex] [wt %] [GPa] [J/g] 0.42 0.1 300 450 135 2590 3.69110.9 47.7 1.81 0.1 133 2720 3.66 114.9 49.6 4.06 0.1 132 2900 3.80116.4 54.5

EXAMPLE 5

As-spun yarn was prepared as described in Example 3, except that thewinding speed was 160 m/min. The as spun properties of this yarn were:linear density 133 dtex, tenacity 1579 mN/tex, modulus 72 Gpa, andtoughness 37 J/g.

This as-spun yarn had an S content of 1.84 wt %, a Cl content of 154ppm, a Na content of 0.06 wt %, and a Ca content of 22 ppm.

This as-spun yarn was heat treated according to Example 4.

Tension in the first oven was 4.47 cN/dtex and in the second oven 0.13cN/dtex.

This resulted in a yarn with a linear density 114 dtex, tenacity 2998mN/tex, modulus 127 GPa, and toughness 51.5 J/g.

This heat treated yarn had an S content of 1.88 wt %, a Cl content of100 ppm, a Na content of 0.07 wt %, and a Ca content of 37 ppm.

EXAMPLE 6

A polymer obtained from a mixture of 40 mole % PPD and 10 mole % DABPI(and 50 mole % TDC) having η_(rel) 6.7 was dissolved in 99.8 wt %sulfuric acid as described in WO 2006/045517. Zone temperatures in thetwin screw extruder were 85° C. The polymer concentration in thesolution was 19 wt %, and the solution was spun through 100 spinningholes of 70 micron. The spinneret assembly was kept at 90° C. The flowwas drawn in an airgap and coagulated in water of 2° C. After washing0.8 wt % NaOH in water was used as neutralizing fluid, and in a secondwashing step the neutralizing fluid was washed off. The yarn was driedat 160° C. and reeled up at 160 m/min to obtain as-spun yarns, and heattreated as in Example 3.

The most essential machine settings and the yarn properties are given inTable 5.

TABLE 5 Tension Tension Linear Breaking Elongation Toughness oven 1 oven1 oven 2 oven 2 density Tenacity at Break Modulus at Rupture cN/dtex °C. cN/dtex ° C. dtex [mN/tex] [wt %] [GPa] [J/g] As-spun properties 2201915 4.6  75    45   1.79 300 0.12 450 199 2310 2.47 137.3 28.6 3.69 3000.11 450 195 2400 2.51 139.3 30.1 5.48 300 0.15 450 196 2360 2.46 139  28.8

EXAMPLE 7

Yarns were spun according to Example 6 from polymers obtained from amixture of 45 mole % PPD and 5 mole % DABPI (and 50 mole % TDC) havingη_(rel) 5.7, giving a linear density of 213 dtex, a tenacity of 2140mN/tex and a modulus of 80 GPa. The most important machine settings andyarn properties are given in Table 6.

TABLE 6 Tension Tension Linear Breaking Elongation Toughness oven 1 oven1 oven 2 oven 2 density Tenacity at Break Modulus at Rupture cN/dtex °C. cN/dtex ° C. dtex [mN/tex] [wt %] [GPa] [J/g] 1.84 300 0.12 450 1961990 2.19 129.8 21.8 2.64 300 0.12 450 194 2000 2.17 131.6 22   3.84 3000.11 450 195 1950 2.11 132.0 20.4 5.18 300 0.10 450 193 2120 2.22 135  23.2

EXAMPLE 8

A polymer obtained from a mixture of 35 mole % PPD and 15 mole % DABPI(and 50 mole % TDC) having η_(rel) 6.4 was dissolved in 99.8 wt %sulfuric acid as described in WO 2006/045517. Zone temperatures in thetwin screw extruder were 85° C. The polymer concentration in thesolution was 20 wt % and the solution was spun through 106 spinningholes of 75 micron. The spinneret assembly was kept at 85° C. The flowwas drawn in an airgap and coagulated in water of 2.5° C. After washing0.8 wt % NaOH in water was used as neutralizing fluid, and in a secondwashing step the neutralizing fluid was washed off. The yarn was driedat 160° C. and reeled up at 160 m/min to obtain as-spun yarns, and heattreated as in Example 3. Before heat treatment the as-spun yarn waspre-dried during 24 hours at 50° C.

The most essential machine settings and the yarn properties are given inTable 7.

TABLE 7 Tension Tension Linear Breaking Elongation Toughness oven 1 oven1 oven 2 oven 2 density Tenacity at Break Modulus at Rupture cN/dtex °C. cN/dtex ° C. dtex [mN/tex] [wt %] [GPa] [J/g] As-spun properties 1901606 4.35  67.7 37.5 0.92 300 0.088 450 169 2590 3.01 131.1 39.1 1.79300 0.082 450 170 2640 3.03 131   39.8 2.74 300 0.065 450 170 2720 3.04134   41.2

The invention claimed is:
 1. A multifilament aramid yarn which has beensubjected to a process of heating the yarn in at least two processsteps, the process of heating comprising: in a first step, heating theyarn at a temperature of from 200 to 360° C. at a tension of at least0.2 cN/dtex; and then in a second step, heating the yarn at atemperature of from 370 to 500° C. at a tension of less than 1 cN/dtex,wherein the tension in the first process step is higher than the tensionin the second process step, wherein the heat processed multifilamaentaramid yarn: has a tenacity of at least 2500 mN/tex and a sulfur contentof at least 0.1 wt %; and comprises a copolymer obtained from a mixtureof monomers comprising DAPBI, an aromatic para-diamine, and an aromaticpara-diacid, wherein at least 12.5 mole % of the monomers is DAPBI, andless than 20 mole % of the monomers is Cl-PPD.
 2. The multifilamentaramid yarn of claim 1, wherein the aromatic para-diamine in the mixtureof monomers is exclusively PPD.
 3. The multifilament aramid yarn ofclaim 1, wherein the yarn is as-spun yarn.
 4. The multifilament aramidyarn of claim 2, wherein the yarn is as-spun yarn.
 5. The multifilamentaramid yarn of claim 1, wherein the yarn is spun from a sulfuric acidspin dope.
 6. The multifilament aramid yarn of claim 2, wherein the yarnis spun from a sulfuric acid spin dope.